What is application layer protocols in TCP/IP?

Transmission Control Protocol/Internet Protocol (TCP/IP) are two different communication protocols. TCP defines the communication in a network and how to send data in the form of packets. IP manages how to make the route for packets to make sure it reaches its defined destination. Before data is sent its IP address is checked then it is determined where to forward the data.

TCP/IP uses the same model as the OSI model. It uses the client/server model type of communication where a user or machine (a client) is provided a service by another computer (a server) in the network.

TCP/IP has four layers − Application Layer, Transport Layer, Internet layer and Network access layer.

Now let us see the different protocols used in the application layer.

Application Layer

It is the top layer of the TCP/IP model. This single layer performs all the operations of a session layer, presentation layer, and application layer of the TCP/IP model.

If the user wants to communicate with various networking systems, this layer combines the functions of interfacing with various applications like, data encoding, data translation and provisions.

Application Layer Protocols

The most used common application layer protocols are explained below:


It is called the terminal emulation protocol. It is used to access the remote end applications. The telnet server that acts as the host initiates a telnet server application to establish a connection with the remote end host called as the telnet client.

After the establishment of connection, it is presented to the OS of the telnet server.

People on the server side use its keyboard and mouse to operate and access the end host with the help of TELNET.

Hypertext transfer protocol (HTTP)

Generally, this protocol is the base of the World Wide Web (WWW). It is used to exchange the hypertext on different systems.

It is a type of request-response protocol.

For example, let us consider an internet explorer which acts as a web client and the application streaming on the PC hosting the website will act as a web server.

Therefore, the server that provides the resources like HTML files and other functions requested by the client that returns a response message to the client which has the content of the completion status data and requested data in the message line.

HTTP resources are recognized on the network by uniform resource locators (URL’s) that deploy uniform resource identifiers (URI) methods HTTP and https.

File Transfer Protocol (FTP)

It is used for sharing or transferring the files between two hosts. The host that runs the FTP application behaves as the FTP server while the other host behaves as the FTP client.

The client host requesting for file sharing requires authentication from the server to access the data.

Once the server authorized this file, it can access any type of files from the server, send or receive files.

Simple mail transport protocol (SMTP)

SMTP is used to send e-mails. We use SMTP to configure the host for sending e-mails.

Domain Name Server (DNS)

Each host device in any network has a unique logical address called the IP address.

IP addresses are a group of numbers and it is difficult to memories. When we type any web address on a browser such as Google.com then we are requesting for a host that has an IP address.

But, there is no need to memories the IP address of the web page that we are requesting for as DNS that maps a name against each logical IP address and stores it.

Therefore, when we are browsing any web page, then it sends the DNS query to its DNS server to map the IP address against the name. Once it gets the address, an HTTP session is built with the IP address.

Dynamic Host Configuration Protocol (DHCP)

The host in any network requires an IP address for communication with the other devices in the network. It gets this address by manual configuration or by using a dynamic host configuration protocol (DHCP).

When we use DHCP, then the host will automatically be assigned with an IP address.

For example, consider a network having 50,000 host devices. Then allocating IP addresses manually to each host is difficult and is time taking too. Therefore, we use the DHCP protocol for assigning an IP address and other information to the connected host devices such as subnet mask IP or gateway IP.